A transcript track can be constructed from a TxDb object.
suppressPackageStartupMessages({
library(TnT)
library(GenomicFeatures)
library(TxDb.Hsapiens.UCSC.hg19.knownGene)
})
txdb <- TxDb.Hsapiens.UCSC.hg19.knownGene
txs <- transcripts(txdb)
txtrack <- TxTrackFromTxDb(txdb, label = "Transcripts", height = 300)
TnTGenome(txtrack, txs[txs$tx_id == 4200])